The proposed conference will be the fourth of a new series of Gordon Conferences on Three-dimensional Electron Microscopy of Macromolecules. Electron microscopy has developed rapidly over the last few years as a tool for structure research at the molecular. Important technical breakthroughs have been made which enable three-dimensional structure to be determined with increasing accuracy, and which have opened the way to a study of structure essentially under controlled physiological conditions. As a result, there are exciting new oprortunities for understanding biological mechanisms and principles of molecular design. The unique position of this series of conferences derives from the fact that they help foster an integrated view of biological complexity, by bringing together scientists working on different levels of the structural hierarchy. The focus of this meeting will be on computational methods and underlying mathematical principles of three-dimensional reconstruction, matching, and refinement in the different size ranges, and on further efforts to perfect the performance of the instrument. Important recent structural findings, relating especially to membrane proteins, viruses, and cell organelles, will also be emphasized. This conference will help catalyze the further development of this field by bringing together many of the key investigators and allowing them to discuss their latest studies and perhaps even incomplete studies in a unique and informal setting. Speakers are being chosen on the basis of the importance of their recent research contributions and the potential of their particular approach in future structure research. Topics to be covered include: cryo-electron microscopy of crystals and single particles, electron crystallography at near-atomic resolution, electron tomography of cell components, methods of three-dimensional reconstruction, visualization of three-dimensional data, design of next-generation instruments, and recent structural results obtained for macromolecular assemblies and viruses.